Can an adult child of the host share the home with the pet sitter?
As in your child staying at the home while the house sitter is present?
Why can’t your child look after the pet and home then. There is no need for a house sitter
Definitely not. No third parties in the home whilst the sit is in progress. Way too many potential risks and conflicts for pets, home and humans. #emptyhomesonlyplease
She’s 21, working, and frequently away, so we need someone who’ll be around on a daily basis.
So just an adult, not a adult child 
But yeah, you can’t have 3rd party people on the property as mentioned by others. It’s not really a fair exchange then
Sounds like you should opt for a paid drop-in service.
Plus, why would you want a stranger in your house with your daughter?
Technically it could work but ONLY if you have a completely separate unit, like an Airbnb unit that has a separate entrance, where your daughter would stay while the sitter stays in the main house with your pets. There are all kinds of homes on THS. There are many renditions of this type of set-up, but the sitter has to have their own space.
@stevemyvr, seems pretty odd that you’d want your 21 year old daughter sharing the home with pet sitters (unless the sitters were well known to you). And why the housesitter would agree to this. Seems lose-lose situation.
That said then we’ve occasionally had situations, typically on long duration sits, where the pet parent has asked us if a family member can stay overnight at the property. We consider each on merits. Both parties understood THS Third Party Policy - housesitter can simply say decline request. Guess if pet parent forces situation then they could terminate the sit.
If that arrangement went ahead and something went awry while the third party was staying, THS would not provide any support because the terms had been breached and both parties had agreed to the arrangement.
Essentially, it would become a private arrangement between the host and the sitter, and THS would not provide any cover or be responsible for any issues that arose.
@stevemyvr think about all the things that could potentially go wrong. Strangers staying in your house with your 21 year old daughter. Glad to know you have so much faith in the sitters. However how do we know she is not going to treat the home like party central while you are away? Or think we are substitute parents who will cook and clean for her? Just a total can of worms. Maybe she could stay with friends or relatives and leave your house empty for the sitters.
Some people may be happy with an adult child, providing they are not dominating the property and keep out of the way as much as possible. I have discovered that many home owners disregard this rule and have not discovered this until on the sit. I did agree in advance once to a young son who was very pleasant and didn’t really see as just in his room for two nights and gone very early in the morning. However other times had about eight uni friends coming and going for at least three days and helping themselves to my food in the fridge. Never knew when coming or going. Had not known until day before they turned up which was towards end of my sit. And last year I had to put up with builders and plumbers coming and going the entire time as well as a daughter who turned up on a couple of occasions. Sent them all away on my last day when discovering plumbers in my unfinished en suite and had no idea they would be there. Owners had given them all keys. I believe the reason I did not receive a review, as were not happy I sent them packing. Also had plumbers refitting a bathroom at another house sit. Various other cases where I have not been informed beforehand. I really think that THS should send out a reminder in bold, when a sit confirmed, that they are not allowed third parties on premises.
If agreed in advance and both are happy then it is not a problem but when you are not informed before commencing a sit, it puts you in a difficult position.
As long as both parties are happy to proceed on the understanding that this would fall outside of the THS terms and therefore be considered a private arrangement. In that situation, THS wouldn’t provide support or cover should anything go wrong, and the THS liability and protections wouldn’t apply to the private arrangement.